No Web site is safe from the kind of massed denial of service attacks that have hit Amazon.com, CNN.com, Buy.com, eBay and Yahoo! this week, the head of security at anti-virus specialist Network Associates' PGP Security unit said yesterday. "At least one person or a group of people have the ability to take down a site at any given time," Jim Magdych told the Dow Jones newswire. "If this is someone who has a large collection of sites waiting to attack, they could literally fire off one attack after another." His chilling prognosis for the Web industry: "They can probably take down pretty much any site on the Internet." Magdych's claim comes after the Amazon.com was hit late yesterday. The e-commerce site didn't go down, but did slow it up. The attack appears to have been a standard denial of service hit, in which hackers attempt to crash a site by flooding it with junk data. What separates the latest attacks from the norm, however, is the apparent use of multiple machines, connected via the Internet and centrally co-ordinated, to hit the hackers are involved -- and perhaps even just a single operator. CNN.com was hit a few hours before the Amazon.com attack. It was left able to provide content but only sporadically. Buy.com, meanwhile, was by a tidal wave of data -- up to 800Mb at its peak -- that brought down it servers for a three-hour period. Online auctioneer eBay also reported a similar attack, which left the site inaccessible to many users and chronically slow to others. That said, eBay has been having so many problems with its servers over the last 12 months, we can't be entirely sure there weren't other problems at play here. All four strikes comes a day after Yahoo! was knocked out for a couple of hours or so through a denial of service attack of its own. At this stage it's not known whether those responsible for the action against Yahoo! also led the attacks yesterday, but the downing of Yahoo! does have the feel of a dry-run about it. ®